Internal combustion engine ignition system with variable timing



May 18, 1965 N. A. JUKES 3,134,640

INTERNAL COMBUSTION ENGINE IGNITION SYSTEM WITH VARIABLE T ING d July 6 File CENERAIUR United States Patent 3,184,649 INTERNAL CGMBUSTlON ENGINE IGNHTION SYSTEM WiTH VARIABLE TIMlNG Norman Alfred dukes, Walsall, England, assignor to Joseph Lucas (Industries) Limited, Birmingham, England Filed July 6, 1962, Ser. No. 237,998 Claims priority, application Great Britain, .luly 12, 1961, 25,1d7/61 1 Claim. (Cl. 315-362) This invention relates to spark ignition apparatus for internal combustion engines of the kind where a continuous advance of timing with engine speed is not required.

The object of the invention is to provide such apparatus in a form whereby the timing may be retarded when desired.

Apparatus according to the invention comprises in combination a generator driven by the engine and arranged to produce during each revolution of the engine a predetermined number of output signals each consisting of successive pulses of opposite polarity, a trigger circuit driven by said output signals and arranged to produce an output pulse on receiving either the positive or the negative pulse of each output signal, a control circuit driven by the trigger circuit for producing a spark, and a reversing switch the position of which determines whether the trigger circuit is driven by the positive or the negative pulse of each output signal of the generator.

An example of the invention is illustrated in the accompanying diagrammatic drawing.

Referring to the drawing, there are provided a pair of terminals 5, 6 for connection to a battery or other D.C. source for supplying power to a trigger circuit and a control circuit, the terminals 5, 6 being of relatively negative and positive polarity in use respectively.

The trigger circuit includes a p-n-p transistor '7 having its emitter connected through a resistor 8 to the terminal 6 and its collector connected to the terminal through a resistor 9 and an ignition switch Ill in series. The base of the transistor 7 is connected to the terminal 6 through a resistor 11 and a diode 12 in series, the diode 12 being bridged by a resistor 13, and moreover the collector of the transistor 7 is connected through a diode 14 to the base of a p-n-p transistor 15, the base being further connected to the terminal 6 through a resistor 16. The

emitter of the transistor 15 is connected to the terminal 6 4 through the resistor 8, Whilst its collector is connected to the terminal 5 through a series circuit including a resistor 17, a diode 18, a resistor 19 and the switch It). The resister 17 and diode 13 are bridged by a capacitor 20 connected across the primary winding 21 of a transformer 22.

The control circuit includes an ignition transformer 23 having a primary winding 24, a secondary winding 25 and a control Winding 26. The primary winding 24 is bridged by a diode 27, and has its ends connected respectively to the terminal 5 and to the collector of a p n-p transistor 28. The emitter of the transistor 28 is connected to the terminal 6, whilst its base is connected to one end of the control winding 26, the other end of which is connected to the terminal 6 through the secondary winding 29 of the transformer 22.

The secondary winding 25 has one end earthed and its other end connected through a distributor 30 to the spark plugs 31 of the engine in turn.

There is further provided a generator 32 driven by the engine and having its output connected through a reversing switch 33 across the resistor 13. The generator 32. may be of any convenient form producing during each revolution of the engine a number of signals dependent on the number of engine cylinders, each signal consisting of a negative pulse followed by a positive pulse. In one form the generator may include a rotor driven by the ddhdfidd Patented May 18, 1965 engine and having thereon, in the case of a four cylinder four-stroke engine, two lobes. Each time a lobe passes a fixed magnetic pick-up coil, it acts in Well-known manner to produce a signal consisting of a negative pulse produced by the leading edge of the lobe, and a positive pulse produced by the trailing edge of the lobe. However, the pulses could be produced by other known means which need not necessarily be magnetically operable.

The operation of the trigger and control circuits is as follows: assuming the switch 16 to be closed, then the transistor 15 is conductive, and the voltage across the resistor 8 holds the transistor 7 non-conductive. Current flows through the transistor 15 to the winding 21, but this current is constant, and hence no output is generated in the winding 29.

In normal operation, the switch 33 is set so that the first pulse in each signal is applied between the base and emitter of the transistor 7, this pulse being of negative polarity so as to render the transistor 7 conductive. As soon as the transistor 7 conducts, the forward bias on the base of the transistor 15 is reduced. This reduces the current flow through the transistor 15, thereby causing a reduction in the voltage across the resistor 8 and permitting a larger current flow through the transistor 7.

'- This regenerative action continues until the transistor 15 is nonconductive, and during the regenerative action the current in the Winding 21 drops sharply to induce a pulse in the winding 29.

The transistor 28 in the control circuit is normally nonconductive. However, when a pulse is received by the winding 29, the base of the transistor 28 is biased to render it conductive, and allow a current to flow to the winding 24. This current in turn induces a voltage in the control winding 26, which biases the transistor 28 further. This regenerative action continues until the core of the transformer 23 is saturated, at which point no further energy is fed back to the transistor 2%, which therefore becomes nonconductive. The rapid rise of current in the winding 24 during the regenerative action induces a high voltage on the winding 25, which is applied through the distributor 30 to a plug 31. Moreover, the back EMF. across the winding 24 upon saturation of the core is prevented from damaging the transistor 28 by the diode 27.

When the negative pulse is no longer present at the base of the transistor '7, the trigger circuit reverts to its original state ready for further operation. The positive pulse following the negative pulse is conducted through the diode 12 and has no efiect.

The lobes are designed to provide a substantial pennanent advance when the switch 33 is in its normal position. However, in order to facilitate starting, the switch 33 is moved to its alternative position. This has the eiiect of reversing the polarities of the pulses in each signal received by the trigger circuit so that the first pulse is positive and has no effect on the trigger circuit. By virtue of the width of the lobe the timing of the engine is less advanced and may if desired be retarded by suitably choosing the width of the lobe. The engine is thus far easier to start.

It will be appreciated that in the example described the trigger circuit is always operated by negative pulses, either the positive or the negative pulse of the generator output being presented to the trigger circuit as a negative pulse depending on the position of the switch 33. However, by employing n-p-n transistors in the trigger circuit the latter could be designed to be operated by positive pulses.

The switch 33 may be manually operable, but preferably is operated automatically upon energisation of the engine starter motor. For this purpose, the moveable parts of the switch 33 can be constituted by contacts connected in circuit with the starter motor so as to be 3 operated by a relay operable at the same time as the starter motor.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is:

An internal combustion engine ignition system comprising in combination a generator driven by the engine, said generator including first and second output terminals and producing between said output terminals during each revolution of the engine a predetermined number of electrical output signals, each output signal consisting of a first pulse of one polarity followed by a second pulse of the opposite polarity, a trigger circuit having first and second input terminals, a reversing switch through which said output terminals of said generator are connected to said input terminals of said trigger circuit, said trigger circuit normally occupying one stable state but being driven to a second state when one of said pulses in each of said signals is applied to the trigger circuit, a spark producing circuit connected to said trigger circuit, said spark producing circuit producing a spark each time said trigger circuit is driven to said second state, said trigger circuit reverting to said one state when the input to said trigger circuit from said generator is removed, and said reversing switch alternatively occupying a first position in which the first output terminal of the generator is connected to the first input terminal of the trigger circuit and the second output terminal of the generator is connected to the second input terminal of the trigger circuit, and a second position in which the first output terminal of the generator is connected to the second input terminal of the trigger circuit, and the second output terminal of the generator is connected to the first input terminal of the trigger circuit.

References Cited by the Examiner UNITED STATES PATENTS 8/62 Quinn 315209 1/63 Kirk 123148 

